U.S. patent application number 12/408031 was filed with the patent office on 2009-12-24 for transmitter, receiver, transmission method and reception method.
This patent application is currently assigned to FUJITSU LIMITED. Invention is credited to Toshio Kawasaki.
Application Number | 20090316813 12/408031 |
Document ID | / |
Family ID | 41046846 |
Filed Date | 2009-12-24 |
United States Patent
Application |
20090316813 |
Kind Code |
A1 |
Kawasaki; Toshio |
December 24, 2009 |
Transmitter, Receiver, Transmission Method and Reception Method
Abstract
A phase relationship between signal sequences obtained by
space-time-coding transmission signals is controlled so as to give
a difference in peak power between the signal sequences to be
transmitted from separate transmission antennas, and either one or
both of the signal sequences are controlled so as to minimize a
rate of a peak power of one of the signal sequences to an average
transmission power of the signal sequences.
Inventors: |
Kawasaki; Toshio; (Kawasaki,
JP) |
Correspondence
Address: |
KATTEN MUCHIN ROSENMAN LLP
575 MADISON AVENUE
NEW YORK
NY
10022-2585
US
|
Assignee: |
FUJITSU LIMITED
Kawasaki-shi
JP
|
Family ID: |
41046846 |
Appl. No.: |
12/408031 |
Filed: |
March 20, 2009 |
Current U.S.
Class: |
375/260 ;
375/295 |
Current CPC
Class: |
H04L 1/0625
20130101 |
Class at
Publication: |
375/260 ;
375/295 |
International
Class: |
H04L 27/28 20060101
H04L027/28; H04L 27/00 20060101 H04L027/00 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 18, 2008 |
JP |
2008-159447 |
Claims
1. A transmitter comprising: a plurality of transmission antennas;
an encoder that performs space-time-coding on transmission signals
to generate signal sequences to be transmitted from the separate
transmission antennas; a phase controller that controls a phase
relationship between the signal sequences obtained through the
space-time-coding so as to give a difference in peak power between
a first signal sequence of the signal sequences to be transmitted
from a first transmission antenna and a second signal sequence of
the signal sequences to be transmitted from a second transmission
antenna; a peak power measurement unit that measures peak power of
the first and second signal sequences whose phase relationship has
been controlled; and a transmission power controller that controls
a transmission power of either one or both of the first and second
signal sequences based on a result of the measurement so as to
minimize a rate of a peak power of one of the signal sequences to
an average transmission power of the first and second signal
sequences.
2. The transmitter according to claim 1, wherein the transmission
power controller decreases a transmission power of either one of
the first and second signal sequences generating a higher peak
power, while increasing a transmission power of the other signal
sequence generating a lower peak power, the first and second signal
sequences being given a difference in the peak power.
3. The transmitter according to claim 2, wherein the transmission
power controller controls the transmission power of the first and
second signal sequences so that a sum of the transmission power of
the first and second signal sequences is constant.
4. The transmitter according to claim 1, wherein the transmission
power controller controls the transmission power so as to satisfy
predetermined conditions under which an orthogonal relationship
between the first and second signal sequences is kept.
5. The transmitter according to claim 4 further comprising a
transmission power control amount notifier that notifies a receiver
receiving the first and second signal sequences of power control
amounts for the transmission power satisfying the predetermined
conditions.
6. The transmitter according to claim 1, wherein the control on the
phase relationship includes a phase control on sub-carriers on
which the signal sequences transmitted from each of the
transmission antennas are mapped.
7. The transmitter according to claim 1, wherein the control on the
phase relationship includes a phase control on orthogonal codes by
which the signal sequences transmitted from each of the
transmission antennas are multiplied.
8. The transmitter according to claim 1 further comprising: a
signal exchanger that exchanges an element signal in the first
signal sequence for an element signal of the second signal sequence
or vice versa between the transmission antennas based on a
relationship of magnitudes between the peak power measured by the
peak power measurement unit so as to satisfy the predetermined
conditions under which the orthogonal relationship between the
first and second signal sequences is kept.
9. The transmitter according to claim 8 further comprising a signal
exchange information notifier that notifies the receiver receiving
the first and second signal sequences of whether or not the signal
exchange has been done.
10. The transmitter according to claim 1 further comprising: a
mapper that maps the first and second signal sequences whose phase
relationship has been controlled onto separate sub-carriers; and an
inverse fast Fourier transform (IFFT) processor that converts the
first and second signal sequences mapped on the sub-carriers into a
time domain; wherein the peak power measurement unit measures peak
power of the first and second signal sequences converted into the
time domain.
11. The transmitter according to claim 1 further comprising a peak
suppressor that performs a peak suppression process on the first
and second signal sequences having undergone the transmission power
control.
12. A receiver comprising: a receiver that receives a signal from a
transmitter controlling a phase relationship between a first signal
sequence transmitted from a first transmission antenna and a second
signal sequence transmitted from a second transmission antenna of
signal sequences obtained by performing space-time-coding on
transmission signals so as to give a difference in peak power
between the first and the second signal sequences; a propagation
path estimator that estimates propagation paths from the respective
transmission antennas based on known reception signals from the
respective transmission antennas; a phase corrector that performs
phase correction according to control information about the phase
relationship on a result of estimation made by the propagation path
estimator; a propagation path compensator that performs propagation
path compensation on a signal sequence received by the receiver
based on a result of estimation corrected by the phase corrector to
separate the signal sequence into signal sequences from the
respective transmission antennas; and a decoder that performs
addition and subtraction on the signal sequences having undergone
the propagation path compensation to decode the signal
sequences.
13. The receiver according to claim 12 further comprising a power
corrector that corrects power of the separated signal sequences
according to power control amounts with which the transmission
power have been controlled in the transmitter so as to satisfy that
the predetermined conditions under which the orthogonal
relationship between the first and second signal sequences is
kept.
14. The receiver according to claim 12, wherein the power control
amounts are notified from the transmitter.
15. The receiver according to claim 12, wherein the transmitter
maps the first and second signal sequences whose phase relationship
is controlled onto separate sub-carriers, converts the first and
second signal sequences into a time domain, and transmits the first
and second signal sequences; and the propagation path compensator
performs the propagation compensation on each of the separate
sub-carriers.
16. The receiver according to claim 12, wherein the propagation
path compensator performs an exchange control on reception signals
to be subjected to the propagation path compensation according to
whether or not an element signal in the first signal sequence and
an element signal in the second signal sequence have been exchanged
for one another between the transmission antennas in the
transmitter so as to satisfy the predetermined conditions under
which the orthogonal relationship between the first and second
signal sequences is kept.
17. A transmission method comprising: performing space-time-coding
on transmission signals to generate signal sequences to be
transmitted from separate transmission antennas; controlling a
phase relationship between a first signal sequence to be
transmitted from a first transmission antenna and a second signal
sequence to be transmitted from a second transmission antenna of
the signal sequences obtained through the space-time-coding so as
to give a difference in peak power between the first and second
signal sequences; measuring peak power of the first and second
signal sequences whose phase relationship has been controlled; and
controlling transmission power of either one or both of the first
and second signal sequences based on a result of measurement so as
to minimize a rate of a peak power of one of the signal sequences
to an average transmission power of the first and second signal
sequences.
18. A reception method comprising: receiving a signal from a
transmitter controlling a phase relationship between a first signal
sequence to be transmitted from a first transmission antenna and a
second signal sequence to be transmitted from a second transmission
antenna of signal sequences obtained by performing
space-time-coding on transmission signals so as to give a
difference in peak power between the first and second signal
sequences; estimating propagation paths from the respective
transmission antennas based on known received signals from the
respective transmission antennas; performing phase correction
according to control information about the phase relationship on a
result of propagation path estimation; performing propagation path
compensation on a received signal sequence based on a result of
propagation path estimation corrected through the phase correction
to separate the received signal sequence into the signal sequences
from the respective transmission antennas; and performing addition
and subtraction on the signal sequences having undergone
propagation path compensation to decode the signal sequence.
Description
CROSS-REFERENCE TO RELATED APPLICATION(S)
[0001] This application is based upon and claims the benefit of
priority of the prior Japanese Application No. 2008-159447 filed on
Jun. 18 2008 in Japan, the entire contents of which are hereby
incorporated by reference.
FIELD
[0002] The embodiment(s) discussed herein is (are) related to a
transmitter, a receiver, a transmission method and a reception
method, and can be used in a technique that performs transmission
with a plurality of transmission antennas.
BACKGROUND
[0003] In wireless communication system, orthogonal frequency
multiplexing such as OFDA (Orthogonal Frequency Division
Multiplexing), OFDMA (Orthogonal Frequency Division Multiple
Access) or the like having excellent use efficiency of frequency,
or orthogonal code multiplexing is sometimes used for the purpose
of efficient use of limited wireless resources such as frequency
resource, for example.
[0004] The orthogonal frequency multiplexing is a system in which
symbol information is mapped on sub-carriers having an orthogonal
relationship to each other in the frequency domain and transmitted.
On the other hand, the orthogonal code multiplexing is a system in
which transmission symbols are made orthogonal, with the use of
codes having an orthogonal relationship to each other such as Walsh
codes, for example, then added (multiplexed) and transmitted.
[0005] These multiplexing system have a disadvantage that a large
peak power can be generated depending on symbol patterns to be
multiplexed, which tends to increase peak-to-average power ratio
(PAPR).
[0006] Meanwhile, a transmission amplifier in a wireless unit in
the wireless communication system is required to have a linear
characteristic in order to prevent the transmission signal from
being distorted. On the other hand, the transmission amplifier is
required to reduce a size thereof and have high efficiency. In
order to satisfy these opposite requirements, it is desired to
reduce the PAPR.
[0007] As a known technique aiming a reduction in PAPR, there is
clipping filter method or the like, which performs a clipping
process on amplitude exceeding a threshold value. As the orthogonal
frequency multiplexing, there are known frequency domain
interleaving method in which symbols to be mapped on sub-carriers
are exchanged in order to reduce the PAPR, PTS (Partial Transmit
Sequences) method in which the phase factor of each sub-carrier is
controlled so as to reduce the PAPR, etc.
[0008] The PTS method divides a sub-carrier used for transmission
of one OFDM symbol into a plurality of groups (clusters), and gives
a different phase rotation to each cluster, which can shift the
peak of each sub-carrier to reduce the peak power.
[0009] As the above techniques aiming a reduction in PAPR, known
are techniques disclosed in Patent Documents 1 to 3 below, for
example.
[0010] [Patent Document 1] Japanese Laid-open Patent Publication
No. 2007-28092
[0011] [Patent Document 2] Japanese Laid-open Patent Publication
No. 2004-173258
[0012] [Patent Document 3] Japanese Laid-open Patent Publication
No. 2001-94530
[0013] The aforementioned clipping filter method has a disadvantage
that the clipping process more than necessary can cause degradation
of the reception characteristic because a non-linear process is
performed in the clipping filter method. The frequency domain
interleaving method and the PTS method increase the amount of
information to be notified to the reception station such as a lot
of interleaving information, information about the phase factors,
etc.
SUMMARY
[0014] According to an aspect of the embodiment, an apparatus
includes a transmitter including a plurality of transmission
antennas, an encoder that performs space-time-coding on
transmission signals to generate signal sequences to be transmitted
from the separate transmission antennas, a phase controller that
controls a phase relationship between the signal sequences obtained
through the space-time-coding so as to give a difference in peak
power between a first signal sequence of the signal sequences to be
transmitted from a first transmission antenna and a second signal
sequence of the signal sequences to be transmitted from a second
transmission antenna, peak power measurement unit that measures
peak power of the first and second signal sequences whose phase
relationship has been controlled, and a transmission power
controller that controls a transmission power of either one or both
of the first and second signal sequences based on a result of the
measurement so as to minimize a rate of a peak power of one of the
signal sequences to an average transmission power of the first and
second signal sequences.
[0015] According to an aspect of the embodiment, an apparatus
includes a receiver including a receiver that receives a signal
from a transmitter controlling a phase relationship between a first
signal sequence transmitted from a first transmission antenna and a
second signal sequence transmitted from a second transmission
antenna of signal sequences obtained by performing
space-time-coding on transmission signals so as to give a
difference in peak power between the first and the second signal
sequences, a propagation path estimator that estimates propagation
paths from the respective transmission antennas based on known
reception signals from the respective transmission antennas, a
phase corrector that performs phase correction according to control
information about the phase relationship on a result of estimation
made by the propagation path estimator, a propagation path
compensator that performs propagation path compensation on a signal
sequence received by the receiver based on a result of estimation
corrected by the phase corrector to separate the signal sequence
into signal sequences from the respective transmission antennas,
and a decoder that performs addition and subtraction on the signal
sequences having undergone the propagation path compensation to
decode the signal sequences.
[0016] According to an aspect of the embodiment, an method includes
a transmission method including performing space-time-coding on
transmission signals to generate signal sequences to be transmitted
from separate transmission antennas, controlling a phase
relationship between a first signal sequence to be transmitted from
a first transmission antenna and a second signal sequence to be
transmitted from a second transmission antenna of the signal
sequences obtained through the space-time-coding so as to give a
difference in peak power between the first and second signal
sequences, measuring peak power of the first and second signal
sequences whose phase relationship has been controlled, and
controlling transmission power of either one or both of the first
and second signal sequences based on a result of measurement so as
to minimize a rate of a peak power of one of the signal sequences
to an average transmission power of the first and second signal
sequences.
[0017] According to an aspect of the embodiment, a method includes
a reception method including receiving a signal from a transmitter
controlling a phase relationship between a first signal sequence to
be transmitted from a first transmission antenna and a second
signal sequence to be transmitted from a second transmission
antenna of signal sequences obtained by performing
space-time-coding on transmission signals so as to give a
difference in peak power between the first and second signal
sequences, estimating propagation paths from the respective
transmission antennas based on known received signals from the
respective transmission antennas, performing phase correction
according to control information about the phase relationship on a
result of propagation path estimation, performing propagation path
compensation on a received signal sequence based on a result of
propagation path estimation corrected through the phase correction
to separate the received signal sequence into the signal sequences
from the respective transmission antennas, and performing addition
and subtraction on the signal sequences having undergone
propagation path compensation to decode the signal sequences.
[0018] The object and advantages of the embodiments will be
realized and attained by means of the elements and combinations
particularly pointed out in the claims.
[0019] It is to be understood that both the foregoing general
description and the following detailed description are exemplary
and explanatory and are not restrictive of the embodiments, as
claimed.
BRIEF DESCRIPTION OF THE DRAWING(S)
[0020] FIG. 1 is a diagram illustrating an example of configuration
of a wireless communication system according to a first
embodiment;
[0021] FIG. 2 is a diagram schematically illustrating an example of
peak power control by a peak power controller illustrated in FIG.
1;
[0022] FIG. 3 is a block diagram illustrating an example of
configuration (in the case of orthogonal frequency multiplexing) of
the peak power controller illustrated in FIG. 1;
[0023] FIG. 4 is a diagram schematically illustrating an example of
the peak power control by the peak power controller illustrated in
FIG. 3;
[0024] FIG. 5 is a block diagram illustrating another example of
the configuration (in the case of orthogonal code multiplexing) of
the peak power controller illustrated in FIG. 1;
[0025] FIG. 6 is a diagram schematically illustrating an example of
the peak power control by the peak power controller illustrated in
FIG. 5;
[0026] FIG. 7 is a block diagram illustrating an example of
configuration (in the case of orthogonal frequency multiplexing) of
a transmitter having the peak power controller illustrated in FIG.
3;
[0027] FIG. 8 is a diagram schematically illustrating an example of
operation of the transmitter illustrated in FIG. 7;
[0028] FIG. 9 is a block diagram illustrating an example of
configuration (in the case of orthogonal code multiplexing) of a
transmitter having the peak power controller illustrated in FIG.
5;
[0029] FIG. 10 is a diagram schematically illustrating an example
of operation of the transmitter illustrated in FIG. 9;
[0030] FIG. 11 is a block diagram illustrating an example of
configuration (in the case of orthogonal frequency multiplexing) of
the receiver illustrated in FIG. 1;
[0031] FIG. 12 is a block diagram illustrating an example of
configurations of propagation path compensators illustrated in FIG.
11;
[0032] FIG. 13 is a block diagram illustrating an example of
configuration (in the case of orthogonal code multiplexing) of the
receiver illustrated in FIG. 1;
[0033] FIG. 14 is a block diagram illustrating an example of
configurations of the propagation path compensators illustrated in
FIG. 13;
[0034] FIG. 15 is a diagram illustrating an example of
configuration of a wireless communication system according to a
second embodiment;
[0035] FIG. 16 is a diagram illustrating an example of a power
control value notifying method by the transmitter illustrated in
FIG. 15;
[0036] FIG. 17 is a block diagram illustrating an example of
configuration of the receiver illustrated in FIG. 15;
[0037] FIG. 18 is a diagram illustrating an example of
configuration of a wireless communication system according to a
third embodiment;
[0038] FIG. 19 is a diagram schematically illustrating an example
of process (in the case where symbols are not exchanged) by a
symbol exchanger in the transmitter illustrated in FIG. 18;
[0039] FIG. 20 is a diagram schematically illustrating an example
of the process (in the case where symbols are exchanged) by the
symbol exchanger in the transmitter illustrated in FIG. 18;
[0040] FIG. 21 is a diagram illustrating an example of method of
notifying of whether symbols have been exchanged or not by the
transmitter illustrated in FIG. 18;
[0041] FIG. 22 is a block diagram illustrating an example of
configuration of the receiver illustrated in FIG. 18;
[0042] FIG. 23 is a block diagram illustrating an example of
configuration of a wireless communication system according to a
fourth embodiment;
[0043] FIG. 24 is a diagram schematically illustrating an example
of operation of the transmitter illustrated in FIG. 23;
[0044] FIG. 25 is a block diagram illustrating an example of
configuration of the receiver illustrated in FIG. 23;
[0045] FIG. 26 is a diagram illustrating an example of
configuration of a wireless communication system according to a
fifth embodiment; and
[0046] FIG. 27 is a block diagram illustrating an example of
configuration of a peak suppressor illustrated in FIG. 26.
DESCRIPTION OF EMBODIMENT(S)
[0047] Hereinafter, exemplary embodiments will be described with
reference to accompanying drawings. The following exemplary
embodiments are merely examples and do not intend to exclude
various modifications and variations to the proposed method and/or
apparatus that are not specifically described herein. Rather,
various modifications and variations may be made to the embodiments
(for example, by combining the exemplary embodiments) without
departing from the scope and spirit of the proposed method and/or
apparatus.
[1] First Embodiment
[0048] FIG. 1 is a diagram illustrating an example of configuration
of a wireless communication system according to a first embodiment.
A system illustrated in FIG. 1 has a one or plural wireless
transmitters (hereinafter, simply referred to as "transmitter") 10,
and one or plural wireless receivers (hereinafter, simply referred
to as "receiver") 50.
[0049] The transmitter 10 can be used in a transmission system of
an entity of a radio access network (RAN) or a transmission system
of a wireless user apparatus. The receiver 50 can be used in a
receiving system of a wireless user apparatus or a receiving system
of an entity of the RAN. These points are the same in the following
descriptions. Reference numeral 51 denotes a reception antenna of
the receiver 50.
[0050] An example of the entity of the RAN is a wireless base
station such as BS (Base Station) or eNB (evolve Node B). An
example of the wireless user apparatus (UE: User Equipment) is a
mobile station such as a cellular phone, an information terminal
with a wireless interface equivalent to the cellular phone, or the
like. Therefore, the UE includes an apparatus that is connected to
a RAN to be able to transmit and receive voice or data, or both.
The UE may be a fixed wireless apparatus (cellular phone, terminal
or the like).
(1.1) Transmitter The transmitter 10 illustrated in FIG. 1 has two
transmission antennas 21-1 and 21-2 (#0, #1) to perform transmitter
diversity with these transmission antennas 21-1 and 21-2. For this
purpose, the transmitter 10 has STC encoders 11-1 to 11-n
corresponding to transmission streams #1 to #n in n sequences (n is
a natural number), and a peak power controller 12.
[0051] The transmitter 10 has multiplexers 13-1 and 13-2,
modulators 14-1 and 14-2, serial/parallel (S/P) converters 15-1 and
15-2, delay circuits 17-1 and 17-2, power controllers 19-1 and 19-2
and transmission devices 20-1 and 20-2, correspondingly to the
respective transmission antennas 21-1 and 21-2. Further, the
transmitter 10 has a peak power measurement device 16 and a control
amount arithmetic processor 18.
[0052] Hereinafter, the transmission antennas 21-1 and 21-2 will be
occasionally referred to as "transmission antenna 21" when not
discriminated from one another.
[0053] The STC encoders 11-i (i=1 to n) perform space-time-coding
(STC) on a symbol sequence of a transmission stream #i which is
input signals. For example, a symbol sequence of the transmission
stream #i is encoded into two symbol sequences whose symbol
information is to be transmitted from the separate transmission
antennas 21-1 and 21-2 at different times, with a plurality (two)
of transmission symbols being a unit (block). Such coding is called
Alamouti Space-Time Block Coding.
[0054] When a transmission signal (symbol) having the symbol number
y (=0, 1, 2, . . . ) in a transmission stream number x (x=1, 2, . .
. , n-1) is expressed as Sxy, for example, two symbols (blocks)
expressed as Sxy and Sx(y+1) are encoded into Sxy and Sx(y+1), and
-Sy(y+1)* and Sxy* by the aforementioned STC, as illustrated in
FIG. 1. Incidentally, A* expresses complex conjugate of A.
[0055] The symbol Sxy is transmitted from one transmission antenna
(first transmission antenna) #0 at a time t, while transmitted from
the other antenna #1 as Sxy* at a time t+1 after one symbol time.
Similarly, the symbol Sx(y+1) is transmitted from one transmission
antenna (second transmission antenna) #1 as -Sx(y+1)* at a time t,
while transmitted from the other transmission antenna #0 at a time
t+1 after one symbol time.
[0056] Namely, a pair of the two symbols Sxy and -Sx(y+1)* are
transmitted from the respective transmission antennas #0 and #1 at
a time t, and a pair of the two symbols Sx(y+1) and Sxy* are
transmitted from the respective transmission antennas #0 and #1 at
a time t+1 after one symbol time. As this, by transmitting the two
transmission symbols from the separate transmission antennas 21
twice for two symbol times, the receiver 50 can obtain a
transmitter diversity gain.
[0057] When attention is given to two symbols Sxy and Sx(y+1)
common to each transmission stream #x, a pair of symbols expressed
as [Sxy, -Sx(y+1)*] can be expressed as (S.sub.0, -S.sub.1*) if
inscription of x is omitted and the magnitude of the symbol number
is expressed with 1 or 0. Similarly, a pair of symbols expressed as
[Sx(y+1) and Sxy*] can be expressed as (S.sub.1, S.sub.0*).
[0058] Therefore, inscription of each of symbols S.sub.0, S.sub.0*,
S.sub.1, -S.sub.1* signifies a symbol block including one symbol or
a plurality of symbols.
[0059] A pair of symbols transmitted for two symbol times is not
limited to the pair illustrated in FIG. 1. For example, when values
of wireless propagation paths (channels) from the transmission
antennas #0 and #1 to the receiver 50 (reception antenna) are
expressed as h0 and h1 and reception signals at the receiver 50
over the respective channels are expressed as r0 and r1, the
reception signals at the receiver 50 can be expressed by the
following equation (1), where a is a constant, and noise components
are omitted.
[ Equation 1 ] ( r 0 r 1 ) = a ( S 0 - S 1 * S 1 S 0 * ) ( h 0 h 1
) ( 1 ) ##EQU00001##
[0060] Accordingly, a pair of symbols transmitted for two symbol
times may be a combination obtained by exchanging lows or columns
for each other in a 4.times.4 matrix in the equation (1), or a
combination obtained by exchanging elements for each other in the
principal diagonal in the matrix.
[0061] The peak power controller 12 performs a process to give a
difference in amplitude value (peak power) between symbols (or
symbol blocks) to be transmitted from the separate transmission
antennas 21 in symbol sequences of each transmission stream #i that
have been space-time-coded as above. In other words, the symbol
sequences that have been space-time-coded as above are processed by
the peak power controller 12 so as to make a pair of symbols to be
transmitted from the separate transmission antennas 21, one of
these symbols having a relatively large peak power resulting from
multiplexing by the multiplexer 13-1 or 13-2, while the other
having a relatively small peak power resulting from multiplexing by
the multiplexer 13-1 or 13-2.
[0062] An example of this process is illustrated in FIG. 2. The
peak power controller 12 performs a process so that the peak power
(PAPR) of a symbol S.sub.0* to be transmitted from one transmission
antenna #1 is relatively smaller (or larger) than the peak power of
a symbol S.sub.0 to be transmitted from the other transmission
antenna #0.
[0063] Similarly, the peak power controller 12 performs a process
so that the peak power (PAPR) of a symbol -S.sub.1* to be
transmitted from one antenna #1 is relatively smaller (or larger)
than the peak power of a symbol S.sub.1 to be transmitted from the
other antenna #0.
[0064] Namely, the peak power controller 12 performs a process so
that a difference in peak power is yielded between the two symbols
S.sub.0 and S.sub.0* having the same information to be transmitted
from the separate transmission antennas #0 and #1. This process can
be attained by controlling the phase relationship of the
transmission symbols between the separate transmission antennas #0
and #1, for example.
[0065] The peak power of each transmission symbol (or symbol block)
having undergone the above process is measured at each of the
transmission antennas #0 and #1, and the transmission power of
either one or both of the transmission signal sequences from the
transmission antennas #0 and #1 is controlled so as to minimize the
PAPR of each of the transmission antennas #0 and #1 on the basis of
a result of the measurement.
[0066] For example, when a symbol that has been found to have a
higher peak power as a result of the measurement is transmitted
from one transmission antenna 21, the transmission power for this
symbol is decreased. And, when a symbol that has been found to have
a lower peak power as a result of the measurement is transmitted
from the other transmission antenna 21, the transmission power for
this symbol is increased. On such occasion, it is preferable to
equalize the peak powers from the transmission antennas #0 and #1.
It is also preferable that a sum of transmission powers of a pair
of two symbols transmitted from the separate transmission antennas
#0 and #1 is constant (that is, it is preferable to control
distribution of the transmission powers of the pair of two
transmission symbols).
[0067] In wireless communication systems, orthogonal frequency
multiplexing using orthogonality of frequency, and orthogonal code
multiplexing using orthogonality of code are known as examples of
transmission signal multiplexing. In the case of orthogonal
frequency multiplexing, the aforementioned peak power control can
be attained by controlling phase factors of sub-carriers on which
signals (symbols) are transmitted (mapped) for each transmission
antenna 21, for example. In the case of orthogonal code
multiplexing, the peak power control can be attained by controlling
the phase factors of the orthogonal codes for each transmission
antenna 21.
[0068] FIG. 3 illustrates an example of configuration of the peak
power controller 12 in the case of the orthogonal frequency
multiplexing, while FIG. 5 illustrates an example of configuration
of the peak power controller 12 in the case of orthogonal code
multiplexing.
(In the Case of Orthogonal Frequency Multiplexing)
[0069] The peak power controller 12 illustrated in FIG. 3 controls
a phase factor of each sub-carrier so that a signal (symbol) to be
transmitted from one transmission antenna #1 differs in peak power
from a signal to be transmitted from the other transmission antenna
#0.
[0070] For this purpose, the peak power controller 12 illustrated
in FIG. 3 has complex multipliers 122-1 to 122-n, each of which
multiplies a signal (sub-carrier) in the n sequences to be
transmitted from the transmission antenna #1 by a phase factor, for
example. Further, the peak power controller 12 has a phase factor
generator 121 which generates a phase factor for each signal
(sub-carrier).
[0071] An example of the phase factors of respective sub-carriers
are given as exp(j.theta.1), exp(j.theta.2), . . . and
exp(j.theta.n), as illustrated in FIG. 3. It is preferable that
values of .theta.1 to .theta.n be known values between the
transmitter 10 and the receiver 50 in order to reduce the amount of
information to be notified from the transmitter 10 to the receiver
50, but not limited to this example.
[0072] From the peak power controller 12 configured as above,
signals to be transmitted from the transmission antenna #0 are
outputted to the multiplexer 13-1 as they remain intact. To the
contrary, each of signals to be transmitted from the transmission
antenna #1 is complex-multiplied by a phase factor exp(j.theta.i)
for a corresponding sub-carrier by the complex multiplier 122-i so
that the peak power of the signals differs from that of the signals
to be transmitted from the transmission antenna #0, and outputted
to the multiplier 13-2.
[0073] In this case, the signals transmitted from the transmission
antenna #0 correspond to a case where the phase factors of all
sub-carriers are 1 because the signals are outputted as they remain
intact, as illustrated in FIG. 4, for example. Accordingly, in the
case where all symbols transmitted from the transmission antenna #0
are 1, a time section in which the peak power is a maximum appears
when the signals having been mapped on the sub-carriers are
converted to the time domain.
[0074] To the contrary, with respect to the signals to be
transmitted from the transmission antenna #1, the phase factors for
the respective sub-carriers to be given to the complex multipliers
122-i are set as illustrated in FIG. 4, for example. In FIG. 4,
attention is given to 16 sub-carriers. When all the symbols are 1,
the peak power of the signals is a minimum in the same time
section, as compared with the peak power of the signals transmitted
from the transmission antenna #0. In other words, the phase factors
are set so as to minimize the peak power.
[0075] In FIG. 4, since attention is given to only part (16
sub-carriers) of the sub-carriers, omitted are waveforms outside a
time section in which the peak power from the transmission antenna
#0 is a maximum (that is, the peak power from the transmission
antenna #1 is a minimum). When the peak power from the transmission
antenna #1 is a maximum in the other time section, the peak power
from the transmission antenna #0 is minimized.
[0076] In the above example, the phase factor control is performed
on a signal on each sub-carrier to be transmitted from the
transmission antenna #1. Alternatively, the phase factor control
may be performed on a signal on each sub-carrier to be transmitted
from the transmission antenna #0. Still alternatively, the phase
factor control may be performed on part of the sub-carriers to be
transmitted from each of the transmission antennas #0 and #1.
(In the Case of Orthogonal Code Multiplexing)
[0077] The peak power controller 12 illustrated in FIG. 5 controls
a phase factor for each orthogonal code so that a signal (symbol)
transmitted from one transmission antenna #1 differs in peak power
from a signal transmitted from the other transmission antenna
#0.
[0078] For this purpose, the peak power controller 12 illustrated
in FIG. 5 has an orthogonal code generator 123 and an orthogonal
phase factor generator 124, for example. Further, the peak power
controller 12 has complex multipliers (orthogonal code multipliers)
125-1 to 125-n for signals in the n sequences to be transmitted
from the transmission antenna #0, and complex multipliers 126-1 to
126-n for signals in the n sequences to be transmitted from the
transmission antenna #1.
[0079] The orthogonal code generator 123 generates orthogonal codes
#1 to #n for signals in the n sequences to be transmitted from the
transmission antenna #0 and for signals in the n sequences to be
transmitted from the transmission antenna #1. As an example of the
orthogonal code, there are Walsh code, Gold code, etc.
[0080] The orthogonal code phase factor generator 124 multiplies
each of the orthogonal codes #1 to #n generated by the orthogonal
code generator 123 by a phase factor so that the peak power
transmitted from the transmission antenna #1 is lower than the peak
power of signals transmitted from the transmission antenna #0.
Whereby, orthogonal codes #1' to #n' having undergone the phase
control according to the phase factors are generated.
[0081] The complex multiplier 125-i complex-multiplies one of the
signals in the n sequences to be transmitted from the transmission
antenna #0 by an orthogonal code #i generated by the orthogonal
code generator 123, and outputs the code to the multiplexer
13-1.
[0082] The complex multiplier 126-i complex-multiplies one of the
signals in the n sequences to be transmitted from the transmission
antenna #1 by an orthogonal code #i' generated by the orthogonal
code phase factor generator 124 and having undergone the phase
control, and outputs the code to the multiplexer 13-2.
[0083] FIG. 6 illustrates an example of operation of the peak power
controller 12, giving attention to the orthogonal codes #1 to #4
for four codes. Since the orthogonal codes #1 to #4, by which
signals to be transmitted from the transmission antenna #0 are
multiplexed, are given to the complex multipliers 125-i as they
remain intact, hence phase factors of the orthogonal codes #1 to #4
correspond to 1 (without phase control).
[0084] FIG. 6 illustrates a state where the orthogonal codes #1 to
#4 are multiplied in each chip time, for example. In this example,
the orthogonal code #1 has a code pattern of (1, 1, 1, 1), the
orthogonal code #2 a code pattern of (1, -1, 1, -1), the orthogonal
code #3 a code pattern of (1, 1, -1, -1) and the orthogonal code #4
a code pattern of (1, -1, -1, 1) in one symbol time (four chip
times).
[0085] On the other hand, the orthogonal codes #1' to #4', by which
signals to be transmitted from the transmission antenna #1 are
multiplied, are generated by setting phase factors, which are to be
multiplied the orthogonal codes #1 to #4, to 1, 1, 1 and -1 by the
orthogonal code phase factor generator 124. Accordingly, the
orthogonal codes #1' to #3' are the same as the orthogonal codes #1
to #3, but the orthogonal code #4' is in a pattern obtained by
multiplying the orthogonal code #4 by -1. Namely, the orthogonal
code #1' has a code pattern of (1, 1, 1, 1), the orthogonal code
#2' a code pattern of (1, -1, 1, -1), the orthogonal code #3' a
code pattern of (1, 1, -1, -1) and the orthogonal code #4' a code
pattern of (-1, 1, 1, -1).
[0086] In the case where symbols of all signals to be transmitted
from the transmission antenna #0 are 1, when the signals multiplied
by the orthogonal codes #1 to #4 are multiplexed, the maximum peak
power appears in a chip time that the signals are multiplied by 1
which is the orthogonal code #i more frequently than in the other
chip times.
[0087] On the other hand, in the case where symbols of all the
signals to be transmitted from the transmission antenna #1 are 1,
when the signals multiplied by the orthogonal codes #1' to #4' are
multiplexed, the number of 1 and the number of -1 multiplied as the
orthogonal code #i are averaged in one symbol time. Therefore, the
peak power of the signals transmitted from the transmission antenna
#1 is minimized in the time domain. In other words, the phase
factors are set so that the peak power is minimized.
[0088] In FIG. 6, omitted are waveforms obtained outside the time
section in which the peak power from the transmission antenna #0 is
a maximum (that is, the peak power from the transmission antenna #1
is a minimum). When the peak power from the transmission antenna #1
is a maximum in another time section, the peak power from the
transmission antenna #0 is a minimum.
[0089] In the above example, phases (code patterns) of the
orthogonal codes, by which signals to be transmitted from the
transmission antenna #1 are multiplied, are controlled. Conversely,
phases of orthogonal codes, by which signals to be transmitted from
the transmission antenna #0 are multiplied, may be controlled.
Alternatively, phases of part of the orthogonal codes of signals to
be transmitted from both the transmission antennas #0 and #1 may be
controlled.
[0090] The peak power controller 12 processes signal sequences to
be transmitted from the transmission antennas 21 so as to yield a
difference in peak power of each symbol (or plural symbols) between
a signal transmitted from the transmission antenna #0 and a signal
transmitted from the transmission antenna #1, and outputs the
signal sequences to the multiplexers 13-1 and 13-2.
[0091] The multiplexers 13-1 and 13-2 each multiplexes
(orthogonal-frequency-multiplexes or orthogonal-code-multiplexes)
signals having undergone the peak power control to be transmitted
from a corresponding transmission antenna #0.
[0092] The multiplexed signal is outputted to a corresponding
modulator 14-1 or 14-2. Each of the modulators 14-1 and 14-2
modulates the multiplexed signal inputted from a corresponding
multiplexer 13-1 or 13-2.
(In the Case of Orthogonal Frequency Multiplexing)
[0093] In the case of orthogonal frequency multiplexing, the
functions of the multiplexers 13-1 and 13-2 and the modulators 14-1
and 14-2 are accomplished with mappers 22-1 and 22-2 and IFFTs
(Inverse Fast Fourier Transformer) 23-1 and 23-2, as illustrated in
FIG. 7, for example. In the case of orthogonal frequency
multiplexing, CP adders 24-1 and 24-2 can be provided in the front
stage of the delay circuits 17-1 and 17-2.
[0094] The mapper 22-1 is inputted thereto one of the n sequences
of STC symbol sequences in two systems obtained by the STC encoder
11-i to map each inputted symbol sequence onto a predetermined
sub-carrier to be transmitted from the transmission antenna #0.
[0095] The mapper 22-2 is inputted thereto signals obtained by
multiplying the other n sequences of the STC symbol sequences by
the above phase factors by the complex multipliers 122-i to map
each inputted symbol sequence onto a predetermined sub-carrier to
be transmitted from the transmission antenna #1.
[0096] Each of the IFFTs 23-1 and 23-2 performs the IFFT process on
a transmission signal in the frequency domain inputted from a
corresponding mapper 22-1 or 22-2 to convert the signal into a
signal in the time domain. The IFFT-processed transmission signals
in the time domain are inputted to the CP adders 24-1 and 24-2,
while inputted to the S/P converters 15-1 and 15-2.
[0097] Each of the CP adders 24-1 and 24-2 adds a cyclic prefix (CP
(also called guard interval)) to the transmission signal in the
time domain obtained by a corresponding IFFT 23-1 or 23-2 in order
to reduce the multi-path interference due to delayed wave. The
transmission signal added CP thereto is inputted to a corresponding
delay circuit 17-1 or 17-2.
(In the Case of Orthogonal Code Multiplexing)
[0098] In the case of orthogonal frequency multiplexing, functions
of the multiplexers 13-1 and 13-2 and the modulators 14-1 and 14-2
are accomplished as a block including adders 25-1 and 25-2, spread
code multipliers 26-1 and 26-2 and a spread code generator 27, as
illustrated in FIG. 9, for example.
[0099] The adder 25-1 adds outputs of the complex multipliers 125-i
illustrated in FIG. 5 to multiplex the outputs. The adder 25-2 adds
outputs of the complex multipliers 126-i illustrated in FIG. 5 to
multiplex the outputs.
[0100] The spread code generator 27 generates predetermined spread
codes. Each of the spread code multipliers (spreader) 26-1 and 26-2
multiplies an output of the corresponding adders 25-1 or 25-2 by
the spread code to perform the spreading process on the
transmission signal. Each of the spread transmission signals is
inputted to a corresponding delay circuit 17-1 or 17-2, while
inputted to a corresponding S/P converter 15-1 or 15-2.
[0101] The S/P converter 15-1 S/P-converts the transmission signal
(modulation signal) modulated by the modulator 14-1 to separate the
signal into symbols. Similarly, the S/P converter 15-2 S/P-converts
the transmission signal (modulation signal) modulated by the
modulator 14 to separate the signal into symbols. The signals
obtained by the S/P converters 15-1 and 15-2 are inputted to the
peak power measurement device 16.
[0102] The peak power measurement device 16 measures a peak power
of each of the symbols (plural symbols) of the modulation signals
inputted from the S/P converters 15-1 and 15-2. A result of the
measurement is given to the control amount arithmetic processor
18.
[0103] The control amount arithmetic processor 18 determines a
transmission power control value to be given to each of the power
controller 19-1 and 19-2 through an arithmetic operation on the
basis of a measurement value of the peak power of each symbol (or
plural symbols) obtained by the peak power measurement device 16.
It is preferable that the transmission power control values be
determined to be values that make the peak powers of signals
transmitted from the transmission antennas #0 and #1 be equal and
minimized. Alternatively, the transmission power control values may
be values that can make a sum of powers of two symbols transmitted
from the transmission antennas #0 and #1 constant.
[0104] Each of the power controllers 19-1 and 19-2 is, for example,
a variable gain amplifier, which performs a transmission power
control on each symbol of the transmission signal (modulation
signal) on the basis of a transmission power control value (gain
control value) determined by the control amount arithmetic
processor 18.
[0105] In the case of orthogonal frequency multiplexing, the
transmission power from the transmission antenna #0 is decreased at
a time t=0 that a symbol S.sub.0 is transmitted from the
transmission antenna #0, while the transmission power from the
transmission antenna #1 is increased (or kept) at a time t=1 that a
symbol S.sub.0* is transmitted from the transmission antenna #1, as
illustrated in FIG. 8.
[0106] In the case of orthogonal code multiplexing, the
transmission power from the transmission antenna #0 is decreased at
a time t=0 that a symbol S.sub.0 is transmitted from the
transmission antenna #0, while the transmission power from the
transmission antenna #1 is increased (or kept) at a time that a
symbol S.sub.0* is transmitted from the transmission antenna #1, as
illustrated in FIG. 10, for example.
[0107] Under such transmission power control, the peak powers from
the transmission antennas #0 and #1 can be minimized.
Alternatively, the transmission powers from the transmission
antennas #0 and #1 can be equal. On such occasion, a sum of
transmission powers of the two symbols (or symbol blocks)
transmitted from the transmission antennas #0 and #1 can be
constant.
[0108] Each of the delay circuits 17-1 and 17-2 delays an input
signal to the power controller 19-1 or 19-2 according to a time
required for the aforementioned peak power measurement and control
amount arithmetic operation, whereby the power control can be
carried out on the transmission signal (symbol) at an appropriate
timing.
[0109] The transmission signals having undergone the above
transmission power control are applied a predetermined wireless
transmission process such as conversion to a wireless frequency
(up-conversion) and the like by the transmission devices 20-1 and
20-2, and transmitted to the receiver 50 from the transmission
antennas 21-1 and 21-2.
[0110] As stated above, the transmitter 10 in this example
space-time-codes the transmission stream #i, and performs a process
(phase control) on each symbol (or symbol block) to yield a
difference in peak power between a symbol sequence transmitted from
one of the antennas 21 and a symbol sequence transmitted from the
other transmission antenna 21.
[0111] Then, the transmitter 10 measures the peak power of each
symbol (or symbol block), and controls the transmission power of
each symbol (or plural symbols) from the transmission antennas 21
according to a result of the measurement so that the peak power of
each of the transmission antennas 21 are minimized.
[0112] Therefore, it is possible to reduce the peak power (PAPR) in
the transmitter diversity communication without applying the
non-linear process such as clipping filter method, and without
increasing information to be informed to the receiving side, unlike
the frequency domain interleaving method or the PTS method. As a
result, it becomes possible to ease the amplification property that
the transmission amplifier in each of the transmission devices 20-1
and 20-2, which is an example of the transmission amplifier is
required, and to attain efficient use of the transmission
amplifier. Further, it becomes possible to decrease the size of the
transmission amplifier and power consumption of the same.
(1.2) Receiver
(In the Case of Orthogonal Frequency Multiplexing)
[0113] FIG. 11 is a block diagram illustrating an example of
configuration of the receiver 50 according to the first embodiment.
The configuration of the receiver 50 illustrated in FIG. 11 is in
the case of orthogonal frequency multiplexing, having a reception
antenna 51, a reception device 52, a timing synchronizer 53, a CP
remover 54, and an FFT (Fast Fourier Transformer) 55, for example.
Further, the receiver 50 has propagation path estimators 56-1 and
56-2, propagation path compensators 57-1 and 57-2, delay circuits
58-1 and 58-2, an adder 59-1, a subtractor 59-2, discriminators
(determination device) 60-1 and 60-2, and a parallel/serial (P/S)
converter 61.
[0114] A wireless signal received by the reception antenna 51 is
subjected to a predetermined wireless reception process such as
low-noise amplification, frequency conversion (down-conversion),
etc. in the reception device 52 to be converted into a base band
signal. The received signal (r0, r1) is expressed by the equation
(1) mentioned hereainbefore, for example.
[0115] The received signal converted into the base band signal is
inputted to both the timing synchronizer 53 and the CP remover 54.
The timing synchronizer 53 detects an OFDM symbol timing of the
received signal inputted from the reception device 52 to establish
the synchronization. The detected symbol timing is given to both
the CP remover 54 and the FFT 55.
[0116] The CP remover 54 removes the CP of the received signal on
the basis of the above symbol timing. The FFT 55 performs the FFT
process on the received signal whose CP has been removed, on the
basis of the above symbol timing, to convert the received signal
into a signal in the frequency domain. The signal in the frequency
domain is inputted to the propagation path estimators 56-1 and
56-2, and the propagation path compensators 57-1 and 57-2.
[0117] The propagation path estimators 56-1 and 56-2, the
propagation path compensators 57-1 and 57-2, the delay circuits
58-1 and 58-2, the adder 59-1 and the subtractor 59-2 together
perform the STC decoding process on the received signal.
[0118] The propagation path estimator 56-1 estimates a wireless
propagation path (channel) value h0 from the transmission antenna
#0 to the reception antenna 51 on the basis of a known received
signal (pilot signal) contained in the received signal in the
frequency domain and transmitted on a sub-carrier assigned to the
transmission antenna #0.
[0119] Similarly, the propagation path estimator 56-2 estimates a
wireless propagation path (channel) value h1 from the transmission
antenna #1 to the reception antenna 51 on the basis of known signal
(pilot signal) contained in the received signal in the frequency
domain and transmitted on a sub-carried assigned to the
transmission antenna #1.
[0120] Each of the propagation path compensators 57-1 and 57-2
gives propagation path compensation to the received signal on the
basis of the channel estimation value h0 or h1 estimated by the
corresponding propagation path estimator 56-1 or 56-2. When the
peak power controller 12 in the transmitter 10 has the
configuration illustrated in FIG. 3, the propagation path
compensator 57-1 complex-multiplies the received signal (r0, r1) by
a channel estimation value h0 by means of a complex multiplier
571-1, thereby to compensate distortion (phase, amplitude) that the
received signal has been subjected along the wireless propagation
path from the transmission antenna #0 to the reception antenna 51.
Whereby, signal components transmitted from the transmission
antenna #0 are detected (separated). The reception signals
(symbols) for two symbol times can be expressed as h0*.times.r0 and
h0*.times.r1.
[0121] On the other hand, the propagation path compensator 57-2 has
a complex multiplier 572-1, a sub-carrier phase setter 572-2 and a
complex multiplier 572-3. The sub-carrier setter 572-2 has the same
phase factor setting for each sub-carrier as the phase factor
generator 121 in the transmitter 10.
[0122] Accordingly, the complex multiplier (phase corrector) 572-3
complex-multiplies the channel estimation value h1 obtained by the
propagation path estimator 56-2 by a phase factor exp(j.theta.i)
given from the sub-carrier phase setter 572-2. Whereby, the phase
control according to the peak power control (phase control) in the
transmitter 10 is performed on the channel estimation value h1 to
correct the channel estimation value h1 according to the phase
control performed in the transmitter 10.
[0123] The complex multiplier 572-1 complex-multiplies the
reception signal (r0, r1) by the corrected channel estimation value
h1 to compensate the distortion (phase, amplitude) that the
reception signal has been subjected along the wireless propagation
path from the transmission antenna #1 to the reception antenna 51.
Whereby, signal components transmitted from the transmission
antenna #1 are detected (separated). The reception signals
(symbols) for two symbol time can be expressed as h1.times.r0* and
h1.times.r1*.
[0124] The reception signal having undergone the
propagation-path-compensation in the propagation path compensator
57-1 is delayed by one symbol time in the delay circuit and
inputted to the adder 59-1, while inputted to the subtractor 59-2
without a delay.
[0125] On the other hand, the reception signal having undergone the
propagation-path-compensation in the propagation path compensator
57-2 is delayed by one symbol time in the delay circuit 58-2 and
inputted to the subtractor 59-2, while inputted to the adder 59-1
without a delay.
[0126] The adder 59-1 adds the reception signal obtained by the
propagation path compensator 57-2 to the reception signal of one
symbol time before obtained by the propagation path compensator
57-1. On the other hand, the subtractor 59-2 subtracts the
reception signal of one symbol time before obtained by the
propagation path compensator 57-2 from the reception signal
obtained by the propagation path compensator 57-1.
[0127] As a result of the above operation, a signal expressed as
h0*.times.r0+h1.times.r1* is obtained at the output of the adder
59-1, while a signal expressed as h0*.times.r1-h1.times.r0* is
obtained at the output of the subtractor 59-2. The former signal
has signal components corresponding to one of the signal sequences
of the STC code, while the latter signal has signal components
corresponding to the other signal sequence of the STC code.
[0128] These signals are discriminated (reception-data-determined)
by the discriminators 60-1 and 60-2, converted into serial signals
by the P/S converter 61, and outputted as reception data. On this
occasion, a signal containing the signal components in the signal
sequences of the transmission STC code, hence transmitter diversity
gain can be obtained.
[0129] In short, a block including the adder 59-1, the subtractor
59-2, the discriminators 60-1 and 60-2 and the P/S converter 61 is
used as an example of a decoder which performs addition and
subtraction on the reception signal sequences having undergone the
propagation path compensation to decode the reception signal
sequences. This point is the same in the following description
unless specifically mentioned.
(In the Case of Orthogonal Code Multiplexing)
[0130] FIG. 13 is block diagram illustrating an example of
configuration of a receiver 50 according to the first embodiment,
in the case of orthogonal code multiplexing. The receiver 50
illustrated in FIG. 13 has, for example, a reception antenna 51,
reception device 52, a searcher 53a, a finger 54a, a replica
orthogonal code generator 55-1 and a code demultiplexer 55-2.
Further, the receiver 50 has propagation path estimators 56-1 and
56-2, propagation path compensators 57-1 and 57-2, delay circuits
58-1 and 58-2, an adder 59-1, a subtractor 59-2, discriminators
(determination device) 60-land 60-2 and a parallel/serial (P/S)
converter 61.
[0131] A wireless signal received by the reception antenna
undergoes a predetermined wireless reception process such as
low-noise amplification, frequency conversion (down-conversion),
etc. in the reception device 52 to be converted into a base band
signal. The reception signal (r0, r1) is expressed by the equation
(1) mentioned hereinbefore.
[0132] The reception signal converted into the base band signal is
inputted to both the searcher 53a and the finger 54a.
[0133] The searcher 53a measures a delay profile of the reception
signal to detect a timing (symbol timing of CDMA symbol) at which
the correlation power is large. The detected timing signal is used
as a despreading timing in the finger 54a. A matched filter or the
like can be used for detection of the correlation power.
[0134] The finger 54a despreads the reception signal on the basis
of the timing signal detected by the searcher 53a.
[0135] The replica orthogonal code generator 55-1 generates a
replica of an orthogonal code used in the transmitter 10.
[0136] The code demultiplexer 55-2 demutliplexes the signal
despread by the finger 54a into reception signals of orthogonal
codes. The despread reception signals of the respective orthogonal
codes are inputted to the propagation path estimators 56-1 and 56-2
and the propagation path compensators 57-1 and 57-2.
[0137] The propagation path estimators 56-1 and 56-2 estimate
channel values h0 and h1 of wireless propagation paths between the
transmission antennas #0 and #1, and the reception antenna 51 from
the reception signals demultiplexed into the orthogonal codes, with
the use of pilot signals of the orthogonal codes assigned to the
respect transmission antennas #0 and #1 in the transmitter 10.
[0138] The propagation path compensators 57-1 and 57-2, the delay
circuits 58-1 and 58-2, the adder 59-1 and the subtractor 59-2
together perform the STC decoding process on the reception
signals.
[0139] In other words, the propagation paths compensators 57-1 and
57-2 perform propagation path compensation on the reception
signals, on the basis of the channel estimation values h0 and h1
estimated by the respective propagation path estimators 56-1 and
56-2.
[0140] In the case where the peak power controller 12 in the
transmitter 10 has the configuration illustrated in FIG. 5, for
example, the propagation path compensator 57-1 complex-multiplies
the reception signal (r0, r1) by the channel estimation value h0 by
means of a complex multiplier 571-1 to compensate distortion
(phase, amplitude) that the reception signal has been subjected
along the wireless propagation path from the transmission antenna
#0 to the reception antenna #0. Whereby, signal components
transmitted from the transmission antenna #0 are detected
(separated). The reception signals (symbols) for two symbol times
can be expressed as h0*.times.r0 and h0*.times.r1.
[0141] On the other hand, the propagation path compensator 57-2 has
a complex multiplier 572-1, a complex multiplier 572-3 and a code
phase setter 572-4. The code phase setter 572-4 is set the same
phase factor setting for each orthogonal code as the orthogonal
code phase factor generator 124 in the transmitter 10.
[0142] The complex multiplier (phase corrector) 572-3
complex-multiplies the channel estimation value h1 obtained by the
propagation path estimator 56-2 by a phase factor given from the
code phase setter 572-4. Whereby, the phase control according to
the peak power control (phase control) in the transmitter 10 is
performed on the channel estimation value h1 to correct the channel
estimation value h1 according to the phase control performed in the
transmitter 10.
[0143] The complex multiplier 572-1 complex-multiplies the
reception signal (r0, r1) by the corrected channel estimation value
h1 to compensate distortion (phase, amplitude) that the received
signal has been subjected along the propagation path. Whereby,
signal components transmitted from the transmission antenna #1 are
detected (separated). The reception signals (symbols) for two
symbol times can be expressed as h1.times.r0* and h1.times.r1*.
[0144] The reception signal having undergone the propagation path
compensation in the propagation path compensator 57-1 is delayed by
one symbol time in the delay circuit 58-1 and inputted to the adder
59-1, while inputted to the subtractor 59-2 without a delay.
[0145] On the other hand, the reception signal having undergone the
propagation path compensation in the propagation path compensator
57-2 is delayed by one symbol time in the delay circuit 58-2 and
inputted to the subtractor 59-2, while inputted to the adder 59-1
without a delay.
[0146] The adder 59-1 adds the reception signal obtained by the
propagation path compensator 57-2 to the reception signal of one
symbol time before obtained by the propagation path compensator
57-1. On the other hand, the subtractor 59-2 subtracts the
reception signal of one symbol time before obtained by the
propagation path compensator 57-2 from the reception signal
obtained by the propagation path compensator 57-1.
[0147] As a result, a signal expressed as h0*.times.r0+h1.times.r1*
is obtained at the output of the adder 59-1, while a signal
expressed as h0*.times.r0-h1.times.r0* is obtained at the output of
the subtractor 59-2. The former signal has signal components
corresponding to one of the signal sequences of the STC code, while
the latter signal has signal components corresponding to the other
signal sequence of the STC code.
[0148] These signals are discriminated by the discriminators 60-1
and 60-2 (reception data determination), converted into serial
signals by the P/S converter 61, and outputted as reception data.
On this occasion, a signal containing the signal components in the
signal sequences of the transmission STC code is composed, hence
the transmitter diversity gain can be obtained.
[2] Second Embodiment
[0149] When the transmission power of each of the transmission
antennas #0 and #1 is independently controlled in the transmitter
10, there is a fear that the orthogonal relationship
(orthogonality) between a symbol transmitted from the transmission
antenna #0 and a symbol transmitted from the transmission antenna
#1 is distorted. In this example, described is a transmission power
control which can prevent degradation of such the
orthogonality.
[0150] When a power control value (control amount) of a symbol
having a symbol number y transmitted from the transmission antenna
#m (m=0, 1) is expressed as kym in common to transmission streams
#1 to #n, the reception signals r0 and r1 at the receiver 50 can be
expressed by the equation (3) and (4) below:
[Equation 2]
r0=h0k00S.sub.0-h1k11S.sub.1*e.sup.(j0) (3)
r1=h0k10S+h1k01S.sub.0*e.sup.(j.theta.) (4)
[0151] These equations (3) and (4) can be changed into equations
(5) and (6) below:
[Equation 3]
h0*k00r0=|h0|.sup.2k00.sup.2S.sub.0-h0*h1k00k11S.sub.1*e.sup.(j.theta.)
(5)
h1k01r1*e.sup.(j.theta.)=h0*h1k01k10S.sub.1*e.sup.(j.theta.)+|h1|.sup.2k-
01.sup.2S.sub.0 (6)
[0152] When an equation (7) below is satisfied, equations (8) and
(9) are established, hence it is found that degradation of the
orthogonality is not generated.
[Equation 4]
k00k11=k01k10 (7)
S.sub.0=(|h0|.sup.2k00.sup.2+|h1|.sup.2k01.sup.2)S.sub.0 (8)
S.sub.1=(|h0|.sup.2k10.sup.2+|h1|.sup.2k11.sup.2)S.sub.1 (9)
[0153] In this example, the control amount arithmetic processor 18
determines the power control values to be given to the power
controllers 19-1 and 19-2 so as to satisfy the relationship of
k00k11=k01k10. The determined power control values can be notified
to the receiver 50. The receiver 50 having received this
notification can carry out appropriate demodulation and decoding
including correction of the channel estimation values, for example,
on the basis of the notified power control values. This
notification can be also done by changing a pattern of the pilot
signal periodically transmitted to the receiver 50, or can be done
with the use of a predetermined channel such as the control
channel.
[0154] FIG. 16 illustrates an example of manner of this
notification. FIG. 16 illustrates a state where pilot signals #0
and #1 of the transmission antennas #0 and #1 and the power control
values are inserted in OFDM symbols of separate sub-carriers in
OFDM frames.
(Transmitter Configuration)
[0155] For this purpose, the transmitter 10 in this example has a
pilot/power control value inserter 27-1 (27-2) between the delay
circuit 17-1 (17-2) and the power controller 19-1 (19-2), which
inserts the pilot signal #0 or #1 and the power control values into
a predetermined OFDM symbol (sub-carrier) in an OFDM frame as
illustrated in FIG. 16, for example.
[0156] The pilot/power control value inserters 27-1 and 27-2 are
used as an example of transmission power control amount notifier
which notifies the receiver 50 of power control values of the
transmission powers satisfying predetermined conditions under which
the aforementioned orthogonal relationship is kept.
[0157] Incidentally, a rule about how the pilot signal #0 or #1 and
the power control values are inserted into an OFDM frame is known
between the transmitter 10 and the receiver 50.
(Receiver Configuration)
[0158] On the other hand, as illustrated in FIG. 17, the receiver
50 performs propagation path compensation (demodulation) on the
reception signals with the use of the channel estimation values h0
and h1 by means of the propagation path compensators 57-1 and 57-2
as described hereinbefore. When the receiver 50 demodulates a
symbol (sub-carrier) in which the power control values have been
inserted, the receiver 50 stores the power control values h0 and h1
in control amount storing devices 62-1 and 62-2.
[0159] For example, power control values k00 and k10 for the symbol
S.sub.0 and S.sub.1 are stored in the control amount storing
devices 62-1, while power control values k11 and k01 for the
symbols S.sub.1* and S.sub.0* are stored in the control amount
storing device 62-2.
[0160] Symbols (sub-carriers) in which data has been mapped are
decoded with the use of power control values stored in the control
amount storing devices 62-1 and 62-2.
[0161] For example, a reception signal (r0, r1) demodulated by the
propagation path compensator 57-1 is multiplied by the power
control amounts k00 and k10 by the complex multiplier 63-1. A
signal obtained as a result of the multiplication can be expressed
as h0*.times.k00.times.r0, h0*.times.k10.times.r1.
[0162] On the other hand, a reception signal (r0, r1) demodulated
by the propagation path compensator 57-2 is multiplied by power
control values k11 and k01 by the complex multiplier 63-2. A signal
obtained as a result of the multiplication can be expressed as
h1.times.k11.times.r0*, h1.times.k01.times.r1*.
[0163] Namely, the complex multipliers 63-1 and 63-2 are an example
of power corrector which corrects a power of each signal sequence
demultiplexed through the propagation path compensation, according
to a power control amount determined when the transmission power
for each transmission antenna 21 is controlled in the transmitter
10 so as to keep the orthogonal relationship.
[0164] The reception signal obtained by the complex multiplier 63-1
is delayed by one symbol time in the delay circuit 58-1 and
inputted to the adder 59-1, while inputted to the subtractor
without a delay.
[0165] On the other hand, the reception signal obtained by the
complex multiplier 63-2 is delayed by one symbol time in the delay
circuit 58-2 and inputted to the subtractor 59-2, while inputted to
the adder 59-1 without a delay.
[0166] The adder 59-1 adds the reception signal obtained by the
complex multiplier 63-2 to the reception signal of one symbol time
before obtained by the complex multiplier 63-1. On the other hand,
the subtractor 59-2 subtracts the reception signal of one symbol
time before obtained by the complex multiplier 63-2 from the
reception signal obtained by the complex multiplier 63-1.
[0167] As a result of the above operation, a signal expressed as
h0*.times.k00.times.r0+h1.times.k11.times.r0* is obtained at the
output of the adder 59-1, while a signal expressed as
h0*.times.k10.times.r1-h1.times.k01.times.r1* is obtained at the
output of the subtractor 59-2.
[0168] The former signal has signal components corresponding to one
of the signal sequences of the STC code, while the latter signal
has signal components corresponding to the other signal sequence of
the STC code. The components of the both signals are signal
components having undergone the transmission power control for each
transmission antennas #0 and #1 so as to keep the orthogonal
relationship between the signals.
[0169] These signals are discriminated by the discriminators 60-1
and 60-2 (reception data determination), converted into a serial
signal by the P/S converter 61, and outputted as reception data. On
this occasion, a signal containing signal components of the signal
sequences of the transmission STC code is composed with the
orthogonal relationship kept, hence excellent transmitter diversity
gain can be obtained.
[0170] Meanwhile, the transmitter 10 may interpolate the pilot
signals into each OFDM symbol (any one of the sub-carriers) at a
timing that the data symbols S.sub.0, S.sub.1, -S.sub.1*, S.sub.0*
are transmitted.
[0171] On such occasion, so long as the transmission powers of the
pilot signal is controlled as well as the above data symbols, the
receiver 50 can obtain information about h0*.times.k00,
h1.times.k11, h0*.times.k10, h1.times.k01, on the basis of the
reception pilot signals.
[0172] Therefore, even when the transmitter 10 does not notify the
receiver of each power control value as above, the receiver 50 can
appropriately demodulate and decode the reception signal with the
above configuration illustrated in FIGS. 11 and 12, for
example.
[3] Third Embodiment
[0173] When the power control values are computed in the
transmitter 10 so as not to degrade the orthogonality of symbols
transmitted from the transmission antennas #0 and #1, there is a
fear that the degree of improvement of the PAPR is degraded
depending on the magnitude relationship between the peak powers of
the transmission symbols. For this reason, this embodiment aims to
decrease the PAPR while keeping the orthogonality.
[0174] The orthogonality can be prevented from being degraded when
the power control values satisfy the conditions [k00k11=k01k10
(therefore, k00/k01=k10/k11)] expressed by the aforementioned
equation (7).
[0175] When above conditions are not satisfied, the transmitter 10
exchanges transmission symbols so as to satisfy the conditions,
thereby to decrease the PAPR.
[0176] FIG. 19 illustrates an example where the transmission symbol
exchanging process is unnecessary. FIG. 19 illustrates a case where
peak powers of symbols S.sub.0 and S.sub.1 to be transmitted from
the transmission antenna #0 are in a relationship of "large
(small)" and "large (small)", and peak powers of symbols -S.sub.1*
and S.sub.0* are in a relationship of "small (large)" and "small
(large)". Since this case can satisfy the conditional equation (7)
of the orthogonality, the control amount arithmetic processor 18
determines power control values k00, k01, k10 and k11 that satisfy
the equation (7) and yield the minimum peak powers.
[0177] FIG. 20 illustrates an example where the transmission symbol
exchanging process is performed. FIG. 20 illustrates a case where
peak powers of symbols S.sub.0 and S.sub.1 transmitted from the
transmission antenna #0 are in a relationship of "large (small)"
and "small (large)", whereas peak powers of symbols -S.sub.1* and
S.sub.0* transmitted from the transmission antenna #1 are in a
relationship of "large (small)" and "small (large)". In this case,
the conditional equation (7) of the orthogonality can not be
satisfied.
[0178] To cope with this, the transmitter 10 performs the process
of exchanging the transmission symbols between the transmission
antennas #0 and #1, and determines power control values k00, k01,
k10 and k11 that satisfy the conditional equation (7) and yield the
minimum peak powers. In the example illustrated in FIG. 20, the
symbol S.sub.1 transmitted from the transmission antenna #0 and the
symbol -S.sub.1* transmitted from the transmission antenna #1 are
exchanged for each other.
[0179] When the above symbol exchanging process is performed, the
transmitter 10 can notify the receiver 50 of this. This
notification can be done by changing the pattern of the pilot
signal periodically transmitted to the receiver 50, or by using a
signal in a predetermined channel such as the control channel.
[0180] FIG. 21 illustrates an example of the notification method
when the pilot signal is used. In FIG. 21, the symbol exchanging
process is not performed on the first and second OFDM symbols,
whereas the symbol exchanging process is performed on the third and
fourth OFDM symbols.
[0181] The transmitter 10 inserts the pilot signals #0 and #1 for
the transmission antennas #0 and #1 at a transmission timing of
each OFDM symbol. On this occasion, the transmitter 10 changes the
pattern of the pilot signal #0 or #1 in an OFDM symbol having
undergone the symbol exchanging process. For example, the
transmitter 10 reverses the polarity (pilot pattern) of the pilot
signal.
[0182] Whereby, the receiver 50 detects whether the symbol
exchanging process has been performed or not by monitoring the
pattern (polarity, for example) of the received pilot signals #0
and #1, thereby to carry out an appropriate receiving process.
(Transmitter Configuration)
[0183] FIG. 18 illustrates an example of configuration of a
transmitter 10 accomplishing the above process. The transmitter 10
illustrated in, for example, FIG. 18 has a symbol exchanger 28 and
a pilot inserter 29-1 (29-2) between the power controller 19-1
(19-2) and the transmission device 20-1 (20-2).
[0184] The symbol exchanger 28 selectively performs a symbol
exchanging process on output signals fed from the power controllers
19-1 and 19-2. Whether the symbol exchanging process is necessary
or not can be determined by the control amount arithmetic processor
18 on the basis of a result of the measurement by the peak power
measurement device 16, for example.
[0185] The symbol exchanger 28 has an S/P converter 281-1 and a P/S
converter 282-1 corresponding to the transmission antenna #0, an
S/P converter 281-2 and a P/S converter 282-2 corresponding to the
transmission antenna #1, and a switch (SW) 283.
[0186] The S/P converter 281-1 (281-2) S/P-converts an output
signal from the transmission power controller 19-1 (19-2), and
outputs one of transmission symbols S.sub.0 and S.sub.1 (for
example, S.sub.0) to the P/S converter 282-1 (282-2), while
outputting the other transmission symbol (for example, S.sub.1) to
the switch 283.
[0187] The switch 283 outputs a symbol inputted from the S/P
converter 281-1 (281-2) corresponding to one #0 (#1) of the
transmission antennas #0 and #1 to the P/S converter 282-2 (282-1)
corresponding to the other transmission antenna #1 (#0) or to the
P/S converter 282-1 (282-2) corresponding to the former
transmission antenna #0, according to a result of the determination
as to whether the symbol exchanging process is necessary or not fed
from the control amount arithmetic processor 18.
[0188] The P/S converter 282-1 P/S-converts an input signal (for
example, S.sub.0) from the S/P converter 281-1 and an input signal
(S.sub.1 when the symbol exchanging is not performed, or -S.sub.1*
when the symbol exchanging is performed) from the switch 283.
[0189] Similarly, the P/S converter 282-2 P/S-converts an input
signal (for example, S.sub.0*) from the S/P converter 281-2 and an
input signal (-S.sub.1* when the symbol exchanging is not
performed, or S.sub.1 when the symbol exchanging is performed) from
the switch 283.
[0190] As above, the symbol exchanging process of exchanging the
transmission symbols between the transmission antennas #0 and #1 is
possible.
[0191] Each of the pilot inserters (signal exchange information
notifiers) 29-1 and 29-2 inserts a pilot signal for the
corresponding antenna #0 or #1 which is in a pattern (polarity)
according to whether the symbol exchanging process has been
performed or not, as illustrated in FIG. 21, for example. The
polarity of the pilot signal to be inserted is controlled on the
basis of a result of the arithmetic operation by the control amount
arithmetic processor 18, for example. Whether the symbol exchanging
process has been performed or not can be notified to the receiver
50.
[0192] The symbol exchanging process on transmission symbols
performed according to a relationship of peak powers of the
transmission symbols between the transmission antennas #0 and #1 as
above can improve the PAPR while preventing degradation of the
orthogonality.
[0193] Notification of the power control values k00, k01, k10 and
k11 from the transmitter 10 to the receiver 50 can be accomplished
in the similar manner to the second embodiment.
(Receiver Configuration)
[0194] The receiver 50 has a configuration as illustrated in FIG.
22, for example. The receiver 50 illustrated in FIG. 22 has a pilot
detector 64 which detects a pilot signal from a reception signal
having undergone the FFT process by the FFT 55. Whether the symbol
exchanging process has been performed or not (the symbol exchanging
process done or not done) in the transmitter 10 can be detected
from the pattern (polarity) of a pilot signal from each of the
transmission antennas #0 and #1 detected by the pilot detector
64.
[0195] According to a result of the detection, the arithmetic
process in the propagation path compensators 57-1 and 57-2 are
controlled. Table 1 below illustrates an example of the
control.
TABLE-US-00001 TABLE 1 Example of propagation path compensation
control (switching) symbols not symbols exchanged exchanged
propagation path h0* .times. r0, h0* .times. r1 h0* .times. r0, h0
.times. r1* compensator 57-1(h0) propagation path h1 .times. r0*,
h1 .times. r1* h1* .times. r0, h1 .times. r1* compensator
57-2(h1)
[0196] As illustrated in Table 1, when the symbol exchanging
process has not been performed, the propagation path compensator
57-1 performs an arithmetic operation expressed by h0*.times.r0,
h0*.times.r1 with the use of the reception signal r0 and r1, and
the channel estimation value h0 obtained by the propagation path
estimator 56-1 to perform propagation path compensation.
[0197] Similarly, the propagation path compensator 57-2 performs an
arithmetic operation expressed by h1.times.r0*, h1.times.r1* with
the use of the reception signal r0 and r1, and the channel
estimation value h1 obtained by the propagation path estimator 56-2
to perform propagation path compensation.
[0198] To the contrary, when the symbol exchanging process has been
performed, the propagation path compensator 57-1 performs an
arithmetic operation expressed by h0*.times.r0, h0.times.r1* with
the use of the reception signal r0 and r1, and the channel
estimation value h0 obtained by the propagation path estimator 56-1
to perform propagation path compensation.
[0199] Similarly, the propagation path compensator 57-2 performs an
arithmetic operation expressed by h1*.times.r0, h1.times.r1* with
the use of the reception signal r0 and r1, and the channel
estimation value h1 obtained by the propagation path estimator 56-2
to perform propagation path compensation.
[0200] As above, when the symbol exchanging process has been
performed in the transmitter 10, the propagation path compensators
57-1 and 57-2 restore the reception symbols to symbols before
having undergone the symbol exchanging process, then perform the
arithmetic operation corresponding to the propagation path
compensation. In other words, the propagation path compensators
57-1 and 57-2 perform a control to exchange the reception signals
that are to undergo propagation path compensation, according to
whether or not the symbol exchanging process has been performed in
the transmitter 10.
[0201] The reception signal having undergone the propagation path
compensation in the propagation path compensator 57-1 is delayed by
one symbol time in the delay circuit 58-1 and inputted to the adder
59-1, while inputted to the subtractor 59-2 without a delay.
[0202] On the other hand, the reception signal having undergone the
propagation path compensation in the propagation path compensator
57-2 is delayed by one symbol time in the delay circuit 58-2 and
inputted to the subtractor 59-2, while inputted to the adder 59-1
without a delay.
[0203] The adder 59-1 adds the reception signal obtained by the
propagation path compensator 57-2 to the reception signal of one
symbol time before obtained by the propagation path compensator
57-1. The subtractor 59-2 subtracts the reception signal of one
symbol time before obtained by the propagation path compensator
57-2 from the reception signal obtained by the propagation path
compensator 57-1.
[0204] The output signal from the adder 59-1 has signal components
corresponding to one of the signal sequences of the STC code, while
the output signal from the subtractor 59-2 has signal components
corresponding to the other signal sequence of the STC code. The
components of the both signals are signal components having
undergone the transmission power control for the respective
transmission antennas #0 and #1 so as to keep a relationship of the
orthogonality between the signals. Note that the arithmetic
operation of the power control values k00, k01, k10 and k11 is
omitted in FIG. 22 (can be the same as the second embodiment).
[0205] These signals are discriminated (reception signal
determination) by the discriminators 60-1 and 60-2, converted into
a serial signal by the P/S converter 61, and outputted as reception
data. On this occasion, the signals containing signal components in
the signal sequences of the transmission STC code are composed with
the orthogonality being kept, hence excellent transmitter diversity
gain can be obtained.
[4] Fourth Embodiment
[0206] FIG. 23 is a block diagram illustrating an example of
configuration of a wireless communication system according to a
fourth embodiment. FIG. 23 illustrates a configuration in the case
where the aforementioned peak power control is applied to an OFDM
transmitter of Space Frequency Block Code (SFBC).
(Transmitter Configuration)
[0207] The transmitter 10 in this example has a phase factor
generator 121, n S/P converters 127-1 to 127-n, n S/P converters
128-1 to 128-n, n complex multipliers 129-1-1 to 129-n-1 and n
complex multipliers 129-1-2 to 129-n-2, as an example of the peak
power controller 12. Further, the transmitter 10 in this example
has mappers 22a-1 and 22a-2 corresponding to the respective
transmission antennas #0 and #1. Note that like reference
characters in FIG. 23 designate like or corresponding parts
described hereinbefore unless specifically mentioned.
[0208] In the peak power controller 12 in this example, the S/P
converter 127-i is inputted thereto one (S.sub.0, S.sub.1, for
example) of two transmission symbol sequences (S.sub.0, S.sub.1 and
-S.sub.1*, S.sub.0*) obtained by a corresponding one of the STC
encoders 11-1 to 11-n to convert the symbol sequence S.sub.0,
S.sub.1 into parallel signals.
[0209] The S/P converter 128-i is inputted thereto the other (for
example, -S.sub.1*, S.sub.0*) of the two transmission symbol
sequences (S.sub.0, S.sub.1 and -S.sub.1*, S.sub.0*) obtained by a
corresponding one of the STC encoders 11-1 to 11-n to convert the
transmission symbol sequence into parallel signals -S.sub.1*,
S.sub.0*.
[0210] The complex multiplier 129-i-1 multiples one (for example,
-S.sub.1*) of the two symbols -S.sub.1*, S.sub.0* obtained by the
S/P converter 128-i by a phase factor corresponding to a
sub-carrier on which this symbol -S.sub.1* is to be mapped by the
mapper 22a-2 among phase factors for respective sub-carriers of the
transmission antenna #1 generated by the phase factor generator
121.
[0211] The complex multiplier 129-i-2 multiplies the other (for
example, S.sub.0*) of the two symbols -S.sub.1*, S.sub.0* by a
phase factor corresponding to a sub-carrier on which this symbol
S.sub.0* is to be mapped among the phase factors of the above
sub-carriers. This phase factor is the same as the phase factor
given to the complex multiplier 129-i-1. Namely, each combination
(-S.sub.1*, S.sub.0*) in the STC coding is complex-multiplied by
the phase factor. Incidentally, the symbol S.sub.0* is mapped on a
sub-carrier (for example, an adjacent sub-carrier) differing from a
sub-carrier on which the symbol -S.sub.1* is mapped.
[0212] The mapper 22a-1 maps the two symbols S.sub.0, S.sub.1
obtained by the S/P converter 127-i on sub-carriers among
sub-carriers assigned to the transmission antenna #0, and outputs a
result of the mapping to the IFFT 23-1. For example, a symbol
sequence S.sub.0 is mapped on an odd (or even) sub-carrier, while
the symbol sequence S.sub.1 is mapped on an even (or odd)
sub-carrier adjacent to the sub-carrier on which the symbol
sequence S.sub.0 is mapped.
[0213] The mapper 22a-2 maps the two symbols -S.sub.1* ,S.sub.0*
which have been complex-multiplied by a phase factor by the complex
multipliers 129-i-1 and 129-i-2 on sub-carriers among sub-carriers
assigned to the other transmission antenna #1, and outputs a result
of the mapping to the IFFT 23-2. For example, a symbol sequence
-S.sub.1* is mapped on an odd (or even) sub-carrier, while the
symbol sequence S.sub.0* is mapped on an even (or odd) sub-carrier
adjacent to the sub-carrier on which the symbol sequence S.sub.0 is
mapped.
[0214] Transmission signals mapped on the sub-carriers for the
transmission antennas #0 and #1 as above undergo the IFFT process
in the IFFTs 23-1 and 23-2 to be converted into signals in the time
domain, are added thereto CP in the CP addition sections 24-1 and
24-2, and inputted to the power controllers 19-1 and 19-2,
respectively.
[0215] On the other hand, outputs from the IFFTs 23-1 and 23-2 are
also inputted to the peak power measurement device 16. The peak
power measurement device 16 measures a peak power of a signal
transmitted from each of the transmission antennas #0 and #1. In
this example, the S/P converters 127-i and 128-i in the peak power
controller 12 S/P-convert the symbols S.sub.0, S.sub.1 to be
transmitted from the transmission antenna #0 and the symbols
-S.sub.1*, S.sub.0* to be transmitted from the transmission antenna
#1, respectively. Therefore, there is no need to again perform the
S/P conversion in order to measure a peak power of each symbol,
unlike the above embodiments.
[0216] FIG. 24 illustrates an example of operation of the
above-mentioned transmitter 10. In this case, with respect to the
signal outputted from the transmission antenna #0, the symbol
sequence obtained by the S/P converter 127-i in the peak power
controller 12 is outputted as it remains intact to the mapper
22a-1, which corresponds to a case where all the phase factors of
sub-carriers assigned to the transmission antenna #0 are 1.
Therefore, in the case where all symbols transmitted from the
transmission antenna #0 are 1, a time section in which the peak
power is a maximum appears when the signal having been mapped on
the sub-carriers is converted into the time domain.
[0217] To the contrary, with respect to a signal transmitted from
the other transmission antenna #1, the phase factors (phase factors
each for a combination in STC coding given to a pair of the complex
multiplexers 129-i-1 and 129-i-2) for sub-carriers assigned to the
transmission antenna #1 are set as illustrated in FIG. 24, for
example. When symbols transmitted from the transmission antenna #1
are 1, the minimum peak power relative to the peak power of the
transmission antenna #0 appears in the same time section. In other
words, the phase factor for each STC code is set so as to minimize
the peak power.
[0218] In this case, in a symbol time that the peak power from the
transmission antenna #0 is a maximum and the peak power from the
transmission antenna #1 is a minimum, the control amount arithmetic
processor 18 determines transmission power control values that
decrease the transmission power from the transmission antenna #0
and increase the transmission power from the transmission antenna
#1. On such occasion, it is preferable that the transmission power
control values make the signals transmitted from the transmission
antennas #0 and #1 have the same and minimum values. Alternatively,
the transmission power control values may be determined as values
that make a sum of powers of two symbols transmitted from the
transmission antennas #0 and #1 constant.
[0219] Conversely, in a symbol time that the peak power from the
transmission antenna #0 is a minimum and the peak power from the
transmission antenna #1 is a maximum, the control amount arithmetic
processor 18 determines transmission power control values that
increase the transmission power from the transmission antenna #0
and decrease the transmission power from the transmission antenna
#1.
[0220] In the above example, the phase factor control is performed
on each sub-carrier of signals transmitted from the transmission
antenna #1. Reversely, the phase factor control may be performed on
each sub-carrier of signals transmitted from the transmission
antenna #0. Alternatively, the phase factor control may be
performed on part of the sub-carriers assigned to each of the
transmission antennas #0 and #1.
(Receiver Configuration)
[0221] FIG. 25 is a block diagram illustrating an example of
configuration of a receiver corresponding to the transmitter 10 of
SFBC. The receiver 50 illustrated in FIG. 25 differs from the
receiver 50 illustrated in FIG. 11 in that the receiver 50 has
propagation path compensators 57A-1, 57B-1, 57A-2 and 57B-2 instead
of the propagation path compensators 57-1 and 57-2, and dispenses
with the delay circuits 58-1 and 58-2. Incidentally, when the
propagation path compensators 57A-1, 57B-1, 57A-2 and 57B-2 are not
discriminated from one another, the propagation path compensator
will be referred to simply as the propagation path compensator
57.
[0222] The propagation path compensators 57 in this example perform
propagation path compensation on sub-carriers adjacent to each
other, corresponding to that a pair of transmission symbol
sequences So and S.sub.1 (or -S.sub.1* and S.sub.0*) are mapped on
sub-carriers adjacent to each other in the transmitter 10.
[0223] For example, when one of the pair of the transmission
sequences S.sub.0 and S.sub.1 (or -S.sub.1* and S.sub.0*) is mapped
on a sub-carrier having an even number while the other transmission
sequence is mapped on a sub-carrier having an odd number, one 57A-1
(57A-2) of the propagation compensators 57A-1 (57A-2) performs
propagation path compensation on the sub-carrier having an even
number, while the other propagation compensator 57A-2 (57B-2)
performs propagation path compensation on the sub-carrier having an
odd number.
[0224] The propagation path compensators 57A-1 and 57B-1 perform
the propagation path compensation on the basis of a channel value
h0 estimated by the propagation path estimator 56-1. The channel
value h0 is estimated by the propagation path estimator 56-1 on the
basis of a pilot signal from the transmission antenna #0.
[0225] The propagation path compensators 57A-2 and 57B-2 perform
the propagation path compensation on the basis of a channel value
h1 estimated by the propagation path estimator 56-2. The channel
value h1 is estimated by the propagation path estimator 56-2 on the
basis of a pilot signal from the transmission antenna #1.
[0226] When a reception signal on a sub-carrier having an even
number is expressed as r0 and a reception signal on a sub-carrier
having an odd number is expressed as r1, the reception signal
having undergone the propagation path compensation by the
propagation path compensator 57A-1 can be expressed as
h0*.times.r0, while the reception signal having undergone the
propagation path compensation by the propagation path compensator
57B-1 can be expressed as h0*.times.r1. On the other hand, a
reception signal having undergone the propagation path compensation
by the propagation path compensator 57B-1 can be expressed as
h1.times.r0*, while the reception signal having undergone the
propagation path compensation by the propagation path compensator
57B-1 can be expressed as h1.times.r1*.
[0227] The reception signal (h0*.times.r0) having undergone the
propagation path compensation by the propagation path compensator
57A-1 and the reception signal (h1.times.r1*) having undergone the
propagation path compensation by the propagation path compensator
57B-2 are inputted to the adder 59-1.
[0228] On the other hand, the reception signal (h1.times.r0*)
having undergone the propagation path compensation by the
propagation path compensator 57A-2 and the reception signal
(h0*.times.r1) having undergone the propagation path compensation
by the propagation path compensator 57B-1 are inputted to the
subtractor 59-2.
[0229] A reason why the delay circuits 58-1 and 58-2 illustrated
in, for example, FIG. 11 are unnecessary is that a pair of
transmission sequences S.sub.0 and S.sub.1 (or -S.sub.1* and
S.sub.0*) are mapped on separate (adjacent) sub-carriers at the
same time.
[0230] Therefore, the adder 59-1 adds the reception signal
(h0*.times.r0) obtained by the propagation path compensator 57A-1
to the reception signal (h1.times.r1*) mapped at the same time and
obtained by the propagation path compensator 57B-2. On the other
hand, the subtractor 59-2 subtracts the reception signal
(h1.times.r0*) mapped at the same time and obtained by the
propagation path compensator 57A-2 from the reception signal
(h0*.times.r1) obtained by the propagation path compensator
57B-1.
[0231] As a result of the above operation, a signal expressed as
h0*.times.r0+h1.times.r1* is obtained at the output of the adder
59-1, while a signal expressed as h0*.times.r1-h1.times.r0* is
obtained at the output of the subtractor 59-2. These signals are
equivalent to outputs from the adder 58-1 and the subtractor 58-2
in the receiver 50 illustrated in, for example, FIG. 11.
[0232] The former signal has signal components corresponding to one
of the signal sequences of the STC code, while the latter signal
has signal components corresponding to the other signal sequence of
the STC code.
[0233] These signals are discriminated (reception data
determination) by the discriminators 60-1 and 60-2, converted into
a serial signal by the P/S converter 61, and outputted as reception
data. On this occasion, a signal containing signal components of
the signal sequences of the transmission STC code, hence
transmitter diversity gain can be obtained.
[5] Fifth Embodiment
[0234] A peak suppressing process, which is a non-linear process,
is not performed in above embodiments. The peak suppressing process
is applicable to each of the embodiments. FIG. 26 illustrates an
example of configuration of the transmitter 10 according to the
first embodiment to which the peak suppressing process is
applied.
[0235] The transmitter 10 illustrated in FIG. 26 has peak
suppressors 30-1 and 30-2 corresponding to the transmission
antennas #0 and #1 between power controllers 19-1 (19-2), and the
transmission devices 20-1 (20-2), respectively. In FIG. 26, like
reference characters designate like or corresponding parts in the
preceding drawings unless specifically mentioned.
[0236] The peak suppressors 30-1 and 30-2 each performs a process
to suppress the peak power of a transmission signal (modulation
signal) having undergone the transmission power control by the
power controller 19-1 or 19-2. As an example of the peak
suppressing process, there is a method of multiplying a factor
(window function) so that the maximum value (peak of amplitude) of
a signal waveform in the time domain of the transmission signal
does not exceed a predetermined threshold value.
[0237] FIG. 27 illustrates an example of configuration of the peak
suppressors 30-1 and 30-2 to which the above-mentioned method is
applied. Each of the peak suppressors 30-1 and 30-2 illustrated in
FIG. 27 has a delay circuit 311, an amplitude arithmetic processor
312, a peak detector 313, a window function generator 314 and a
multiplier 315, for example.
[0238] The delay circuit 311 delays a transmission signal inputted
from the power controller 19-1 or 19-2 by a predetermined time to
adjust a timing at which the multiplier 315 multiplies the
transmission signal by a factor given from the window function
generator 314.
[0239] The amplitude arithmetic processor 312 samples a waveform of
the transmission signal inputted from the power controller 19-1 or
19-2 at predetermined sampling intervals to discretely detect
amplitude values of the transmission signal.
[0240] The peak detector 313 detects the maximum value (peak) of
the amplitude values of the transmission signal and the sampling
timing of the same from distribution of the amplitude values
obtained by the amplitude arithmetic processor 312.
[0241] The window function generator 314 generates a factor (window
function) having an appropriate distribution which decreases an
amplitude level of the maximum value in order to decrease the
maximum value detected by the peak detector 313 to a predetermined
threshold value or below. As the window function, applicable is an
arbitrary window function such as cosine function, raised cosine
function, Hunning window, Humming window, Kaiser window or the
like.
[0242] The multiplier 315 multiplies the transmission signal
delayed in the delay circuit 311 by the function generated by the
window function generator 314 to suppress the peak of the
transmission signal. Whereby, the improvement of the PAPR can be
further increased.
[0243] The transmission signal having undergone the peak
suppressing process undergoes a predetermined wireless transmission
process in the transmission device 20-1 or 20-2, and transmitted
from the transmission antenna #0 or #1 to the receiver 50.
[0244] The peak suppressing process can be done with a filter such
as a clipping filter.
[0245] All examples and conditional language recited herein are
intended for pedagogical purposes to aid the reader in
understanding the invention and the concepts contributed by the
inventor to furthering the art, and are to be construed as being
without limitation to such specifically recited examples and
conditions, nor does the organization of such examples in the
specification relate to a illustrating of the superiority and
inferiority of the invention. Although the embodiment(s) has (have)
been described in detail, it should be understood that the various
changes, substitutions, and alterations could be made hereto
without departing from the sprit and scope of the invention.
* * * * *